Analysis of domoic acid and isomers in seafood by capillary electrophoresis

Methods for the analysis of domoic acid (DA) based upon capillary electrophoresis (CE) combined with UV absorbance detection were investigated. DA could be analyzed using bare fused-silica capillaries in either the cationic or anionic mode with acidic or basic buffer systems, respectively. Highest performance, in terms of both separation efficiency and analysis time, was achieved with phosphate or borate buffers at a pH of approximately 9. The addition of beta-cyclodextrin to the borate buffer permitted a separation of DA and several of its isomers (isodomoic acids) that was superior to that achieved with liquid chromatography (LC). The optimum background electrolyte for the separation was 22.5 mM sodium tetraborate at pH 9.2 with mM beta-cyclodextrin. In addition, an extraction and clean-up procedure was developed and tested with mussels, clams and anchovies. Aqueous methanol extraction of samples followed by a tandem strong anion and strong cation exchange clean-up provided an extract that was completely compatible with CE analysis. A mass detection limit of 3 pg of DA injected and a method detection limit of 150 ng/g in tissues could be achieved. Comparison with LC showed that comparable precision and accuracy could be attained by the two techniques.